The present invention relates to the field of wireless communication. The present invention especially relates to a method of transmitting data signals, a method of receiving data signals, a first device for transmitting data signals and a second device for receiving data signals.
FIG. 1 depicts for illustrative purposes a wireless communication network 102 employing spatial diversity relying on the use of a plurality of transmission paths between communicating devices. More particularly, network 102 illustrates a 60 GHz (millimeter band) radio transmission system well suited to very high bit rate data transmission as for example video distribution.
Network 102 comprises a first device 110 that represents a data source node and a second device 120 that represents a data destination node. In this particular example, the second device 120 is composed of a communication device 190 connected to the wireless network and of a display device 180 connected to the communication device 190 for rendering the received data content, e.g. displaying the video. It is to be noted that the first device 110 may also represent a data relay node instead of being the originator of the data, the data source node being then represented by another device 100 belonging to the communication network. It is common to have a meshed network comprising relay nodes for relaying data between different devices to cope with the short range of the millimeter waves.
A transmitted signal from first device 110 may reach second device 120 through a line-of-sight (LOS) transmission path A if it is not blocked by any obstacle. In addition, the signal may be reflected by objects 115 which may cause a plurality of non line-of-sight (NLOS) transmission paths B, C and D.
It is known in the state of the art to use narrow beam steering antennas 111, 121 both at the first device 110 when emitting a signal and at the second device 120 when receiving the signal. Steering an antenna to a given orientation corresponds to configuring its parameters (for example the weighting coefficients associated with the elements of an antenna array) such that the radiation of the signal, in case of emission, or the antenna sensitivity, in case of reception, is accentuated in that given direction relatively to other directions. This has the advantage of providing high antenna gains and allowing the fulfillment of link budget requirements for high bit rate applications as video distribution.
In such a situation, both narrow beam antennas 111, 121 have to be steered to an orientation that corresponds to one given transmission path. This latter could be either a LOS transmission path or a NLOS transmission path as depicted in FIG. 1 for transmission paths A and B. Synchronization between the two devices is thus needed regarding which transmission path to use and appropriate configuration of their corresponding antennas is necessary to orientate the two beams in the right directions.
This problem becomes critical when very short time is available for finding and/or agreeing on the transmission path to use. Indeed, even if a full scan is performed in three dimensions for searching for all possible paths beforehand, these transmission paths may not be available or valid when the communication actually starts because of the moving obstacles that may interrupt the communication or because the objects 115 over which signals are reflected have been displaced. Communicating devices should then be able to adjust transmission paths used as a function of the network environment so that to always maintain acceptable communication quality.
In addition, there may be a need to change the transmission path used from one communication to another regardless of the knowledge on whether the initially used transmission path is still valid or not. This has the advantage of introducing spatial diversity and thus making the communication more robust against transmission errors or data loss that may result from noise or from obstacles in one of the transmission paths.
For example, one can use a technique of transmitting a video alternatively through different transmission paths in conjunction with concealment mechanisms. Video lines 1, 2, 3, 4, 5, . . . may be successively transmitted along available transmission paths A, B, C and D (line 1: A, line 2: B, line 3: C, line 4: D, line 5: A, etc.). Thus, if one path is disrupted, only 1 line over M (M equals to 4 in the above example) is lost, and the full video can be reconstructed based on the other correctly received lines using concealment mechanisms (duplication from the previous line, or pixels averaging from adjacent received pixels, . . . ).
Nevertheless, in order to use such technique, communicating devices should agree on the transmission path they have to use at each communication.
This is particularly true for a synchronous communication channel implementing a time division multiplexing (TDM) for sharing communication channel access between different communicating devices. In TDM, as depicted by FIG. 2, time domain is divided into a plurality of time slots 214, 221, 222, . . . , 224, 231. Each emitting device is allotted one time slot periodically in each cycle 210, 220, 230 for emitting its signal towards a receiving device using for example a given transmission path. A difficulty is then to be able to swiftly determine and associate a reliable transmission path with each time slot.
Moreover, using an antenna beam that is steerable in three dimensions (3D) advantageously increases the chances of finding many transmission paths (all objects including walls, ceiling and floor can then be acting as reflecting objects 115), but at the same time renders the implementation of searching for/updating of the set of all possible transmission paths more difficult because of the required time for doing the search.
The invention in at least one of its embodiments is aimed at overcoming these different drawbacks of the prior art.
More specifically, an objective of at least one embodiment of the invention is to provide a technique for determining transmission paths for a first and a second device for communicating via narrow beam antennas (referred to as point-to-point communication mode) when using a synchronous wireless communication channel implementing a time division multiplexing (TDM) scheme.
It is another goal of at least one embodiment of the invention to provide a technique of this kind that makes it possible to configure the orientations of the antennas beams at the emitting (first) and receiving (second) devices corresponding to transmission paths parameters.